Term Test 3B
Instructor: Dr. Robert Davis
Chemistry 1050
Name: _____________________
Wednesday, November 17, 2011
ANSWER THE TEST QUESTIONS IN THE SPACE PROVIDED.
MARKS WILL BE DEDUCTED FOR INCORRECT USE OF SIGNIFICANT FIGURES
AND FOR LACK OF UNITS IN CALCULATIONS.
Marking Scheme
Question
Value
Part A: Short Answer Questions
A1 – A4
12
Part B: Longer Answer Questions
B1
12
B2
7
B3
4
B4
4
B5
3
B6
1
B7
2
Total
45
% Grade
1
Mark
Part A: Short Answer Questions
[Value]
[3]
[3]
[2]
[4]
A1.
A2.
A3.
A4.
Define or explain
(a)
anti-bonding molecular orbital
(b)
sigma bond
(c)
formal charge
Give an example of
(a)
a tetrahedrally shaped molecule _________________________
(b)
a trigonal pyramidal molecule _______________________
(c)
a see saw shaped molecule __________________________
List the following molecules in order of decreasing bond polarity
(a)
PCl3, PBr3, PI3 most polar ____ ____ ____ least polar
(b)
Cl2, HCl, NaCl, ClBr most polar ____ ____ ____ ____ least polar
Calculate a ΔHo value for the reaction
H2C=CH2(g) + Cl2(g)
→
H2ClC–CH2Cl(g)
using the bond energies: C–H ( 414 kJ mol–1), C=C ( 611 kJ mol–1), Cl–Cl
( 243 kJ mol–1), C–C (347 kJ mol–1), and C–Cl ( 339 kJ mol–1).
2
Part B: Longer Answer Questions
[Value]
[12]
B1.
Complete the following table.
Species
BeF2
SeCl4
Lewis structure
Sketch of shape
Name of shape
Approximate bond
angles
Indicate if the
species is polar or
non–polar
3
XeF4
[7]
B2.
Construct a molecular orbital energy level diagram for the O2+
homonuclear diatomic species. Consider only the valence shell electrons.
Determine whether the species is diamagnetic or paramagnetic. Calculate
the bond order.
B3.
(a)
Draw two “equivalent” resonance structures for the NO2Cl
molecule.
(b)
What is the bond order in this molecule?
(c)
What is the formal charge on N in this molecule?
.
[4]
4
[4]
B4.
Balance the following oxidation-reduction reaction taking place in acidic
solution.
Cr2O72–(aq) + Fe2+(aq)
[3]
[1]
B5.
B6.
→
Cr3+(aq) + Fe3+(aq)
Give chemical formulas for molecules not containing carbon where the
central atom exhibits
(a)
sp hybridization
(b)
sp2 hybridization
(c)
sp3 hybridization
Draw a picture representing the shape of one  bond in H–C≡C–H
(acetylene).
5
[2]
B7.
Indicate whether a sp, sp2 or sp3 hybridization scheme should be used to
describe the bonding at each C, O and N atom in the molecule
represented below.
O
H C C C
NH2
6